The present embodiments relate to integration of imaging systems, specifically magnetic resonance (MR) imaging and positron emission tomography (PET) systems.
PET imaging yields quantitative measures of metabolic and dynamic processes. PET imaging relies on the positron emitting decay of a radioactive tracer isotope attached to a biologically active compound. The subsequent annihilation of the positrons with electrons generates pairs of high-energy photons travelling near opposite directions. These events are detected when the photons reach a detector of the PET system. Unfortunately, the photons can be absorbed by tissue, particularly bone. This absorption is referred to as attenuation and leads to an undesirable intensity distortion in PET images.
Raw PET data is often corrected for photon attenuation and scatter. Attenuation correction typically uses data acquired from a separate measurement. One common approach uses computed tomography (CT) data provided by a combined PET/CT scanner. Other clinical scanners provide concurrent PET and magnetic resonance (MR) imaging. Use of MR data for attenuation correction advantageously avoids the radiation dose involved in CT scans. A typical MR/PET workflow may thus begin with concurrent PET scanning and MR scanning for attenuation correction. After the MR attenuation correction scan is complete, further MR scanning is often conducted for diagnostic purposes while the PET scan continues.
Patient motion during PET acquisition complicates attenuation correction. If there is patient motion during the PET scanning, the lack of spatial registration between PET and MR attenuation correction data may result in poor image quality. If an operator of the MR/PET system is made aware of the patient motion, another MR attenuation correction scan may be conducted at the end of the PET scan. The operator then visually compares non-attenuation corrected PET images with the two MR attenuation correction scans to manually select the MR data to be used for attenuation correction of the PET data. This approach is undesirably time consuming and subjective.